1. TECHNICAL FIELD
This invention relates to a two-speed stepper actuator for rotationally driving a member such as a paper machine headbox slice opening control spindle. The driven spindle is one of a plurality that are evenly distributed across the width of the slice for acting on the control lip of the slice. More particularly, the invention relates to a stepper actuator for rotationally driving the spindles individually in ratchet-like fashion at two speeds, one for "macromotion" of, perhaps, 16 micron of slice lip travel and another for "micromotion" of, perhaps 1 micron of slice lip travel.
2. BACKGROUND ART
The slice opening of a headbox on a paper machine meters flow of the pulp slurry or stock in the headbox onto the fourdrinier wire. A number of rotationally driven spindles, perhaps 50 to 60, are connected to a headbox control lip to vary the metering opening transversely across the machine. The spindles typically are threadedly attached at their upper ends to rotationally driven power nuts which linearly drive the individual spindles in known manner. The two speed stepper actuator of the invention drives the power nuts in a ratchet-like rotational fashion to accomplish the linear spindle motion at either of two speeds.
The rotationally driven power nuts have largely replaced manually adjusted spindles or jack screws on paper machines because they provide for increased linear sensitivity for slice lip adjustment purposes. It has been known to equip each spindle or jackscrew with a separate driving motor and gear reducer. The advantage of being able to power the spindle at a macromotion rate and then to finely adjust the slice lip opening by means of micromotion has not heretofore been available in a stepper actuator. The present invention thus provides a needed device for fast and accurate control of the slice lip of a headbox.